Synthesis of Reactive Disperse Dyes for Dyeing Natural Fabrics in Supercritical CO2

Over the course of time, the dyeing industry has become one of the greater polluters of water worldwide. The sheer volume of water and the high concentration of additives used in textile colouration are staggering, which have already caused unrepairable damage to environment and continue to directly impact on the sustainability of textile colouration industry. “Supercritical CO2 dyeing” uses supercritical CO2 as the dyeing medium, enabling the reduction and even elimination of the creation of textile colouration wastewater. Supercritical carbon dioxide (scCO2) has a low critical point and is non-flammable. It can be recycled, providing a promising environmentally friendly substitute for aqueous media. Reactive disperse dyes that have both reactivity towards natural fabrics and high solubility in scCO2 would offer great promise for colouring natural fabrics. In this study, the isocyanate group, as a reactive group, was introduced to disperse dyes to create reactive disperse dyes suitable for supercritical dyeing. Thus, a series of reactive disperse dyes, containing both isocyanate groups and alkyl groups were successfully synthesised. Dyeing experiments under different dyeing conditions were performed to establish the optimal dyeing conditions for these synthesised dyes. A new synthesis route was developed to create an azo-based disperse reactive dye containing the vinyl sulphonyl reactive group, which was used to dye natural fibres using scCO2 as the dyeing medium. Using relatively moderate, optimal conditions in the scCO2 dyeing processes, uniform dyeing with high colour strength and fastness properties that were similar to those from conventional aqueous dyeing were achieved on natural fabrics that were dyed with the synthesised dyes. Furthermore, there are opportunities to modify a wide range of disperse dyes following this synthesis route.